Identification and characterization of alphavirus M1 as a selective oncolytic virus targeting ZAP-defective human cancers

Oncolytic virotherapy is a growing treatment modality that uses replicating viruses as selective antineoplastic agents. Safety and efficacy considerations dictate that an ideal oncolytic agent would discriminate between normal and cancer cells on the basis of common genetic abnormalities in human cancers. Here, we identify a naturally occurring alphavirus (M1) as a novel selective killer targeting zinc-finger antiviral protein (ZAP)-deficient cancer cells. In vitro, in vivo, and ex vivo studies showed potent oncolytic efficacy and high tumor tropism of M1. We showed that the selectivity depends on ZAP deficiency by systematic identification. A large-scale multicenter pathology study using tissue microarrays reveals that ZAP is commonly deficient in human cancers, suggesting extensive application prospects for M1. Additionally, M1 killed cancer cells by inducing endoplasmic reticulum stress-mediated apoptosis. Our report provides novel insights into potentially personalized cancer therapy using oncolytic viruses.Despite advances in cancer therapy over the past few decades, cancer is still a major health problem all over the world (1). One innovative class of targeted anticancer strategies is the use of replicating oncolytic viruses with selective tropism for cancerous cells and tissues (2, 3). The tumor selectivity of oncolytic virus is primarily based on the genetic abnormalities of malignant cells, including innate immune defects, aberrant oncogenic signaling, and tumor-specific receptors (4–6). The thriving viruses in tumor cells may lead to direct cell lysis, anticancer immune response, or modulation of tumor vasculature (3, 7). Moreover, some of the cancer-targeted multimechanistic oncolytic viruses have been proven to be well-tolerated in clinical trials, with patients exhibiting only mild flu-like symptoms, offering great potential for increasing efficacy while eliminating the side effects (8). To date, several oncolytic viruses have been tested in preclinical and clinical trials, of which the milestone is a pivotal phase III trial using talimogene laherparepvec for unresected melanoma (2, 3, 9). Although a few therapeutic viruses are performing well in clinical trials, not all patients showed good response. Novel oncolytic viruses that grow better in some cancer cells in a predictable manner remain to be discovered for potentially personalized cancer therapy.M1 is a strain of Getah-like alphavirus that was isolated from culicine mosquitoes collected on Hainan Island of China (10, 11). Getah virus is transmitted mainly among horses and pigs, and it has not been linked to human illness (12–14). Also, M1 does not cause apparent disease symptoms in mice or rats, even on administration of doses up to 3 × 10⁷ pfu per mouse or 3 × 10⁸ pfu per rat. Earlier, we reported that M1 induces apoptosis in glioma cells (10). Thus, we hypothesized that an apathogenic cancer cell-killing virus could be a candidate for systemic oncolytic therapy.In this study, we sought to investigate the anticancer effectiveness and tumor tropism of M1 and uncover the mechanisms, aiming to identify a candidate for personalized oncolytic virotherapy.